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最新推荐文章于 2024-12-18 17:34:45 发布

转载最新推荐文章于 2024-12-18 17:34:45 发布 · 70 阅读

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原文链接：http://www.cnblogs.com/dingyunfeng/p/10714250.html

本文深入探讨了二分查找、快速排序等经典算法的实现原理及应用，对比了不同算法的时间复杂度，并通过具体代码示例展示了算法的运行过程。

常用算法

# 二分查找
@cal_time
def bin_search(li, val):
    low = 0
    high = len(li)-1
    while low <= high: # 只要候选区不空,继续循环
        mid = (low + high) // 2
        if li[mid] == val:
            return mid
        elif li[mid] < val:
            low = mid + 1
        else: # li[mid] > val
            high = mid - 1
    return -1

@cal_time
def sys_search(li, val):
    try:
        return li.index(val)
    except:
        return -1

li = list(range(0,20000000,2))

sys_search(li, 20000001)

def _quick_sort(li, left, right): #快速排序方法1
    if left < right: # 待排序的区域至少有两个元素
        mid = partition(li, left, right)
        _quick_sort(li, left, mid-1)
        _quick_sort(li, mid+1, right)

@cal_time
def quick_sort(li):
    _quick_sort(li, 0, len(li)-1)


def partition(li, left, right):
    tmp = li[left]
    while left < right:
        while left < right and li[right] >= tmp:
            right -= 1
        li[left] = li[right]
        while left < right and li[left] <= tmp:
            left += 1
        li[right] = li[left]
    li[left] = tmp
    return left

def _quick_sort2(li):#快速排序方法2
    if len(li) < 2:
        return li
    tmp = li[0]
    left = [v for v in li[1:] if v <= tmp]
    right = [v for v in li[1:] if v > tmp]
    left = _quick_sort2(left)
    right = _quick_sort2(right)
    return left + [tmp] + right

import copy

li = list(range(100000))
random.shuffle(li)
li2 = copy.copy(li)
quick_sort(li)
quick_sort2(li2)

# 最好情况O(n) 平均情况O(n^2) 最坏情况O(n^2)

@cal_time
def bubble_sort(li):
    for i in range(len(li)-1):  # i表示第n趟 一共n或者n-1趟
        exchange = False
        for j in range(len(li)-i-1): # 第i趟 无序区[0, n-i-1]  j表示箭头 0~n-i-2
            if li[j] > li[j+1]:
                li[j], li[j+1] = li[j+1], li[j]
                exchange = True
        if not exchange:
            break


li = list(range(10000))
random.shuffle(li)
bubble_sort(li)

转载于:https://www.cnblogs.com/dingyunfeng/p/10714250.html